POWER GENERATION AND TRANSMISSION
kilowatt-hour: the vacuum, however, was concurrently increased from 25 to 28 The diagram shows the economy curve of a low-pressure turbine used with a
regenerator (equalizer and storage tank for the steam), having an inlet pressure of 15 to 16K lb. absolute with 25- to 27-in. vacuum.
Extraction Turbines discharge some of the steam from between pressure
i.P -Hour at Switchboard £ g 8 II II III II IIIIIH |l|||| ----------- __ CURVE OF STEAM CONSUMPT1 >« ........ RATE AU STEAM TURBINE .2^ --------- INTERNATIONAL HARVESTER ...... ^j ---------------- ....... - ------------------ +H-— ::::::- ----------- ON -T; ------ ..... ------- CO. ------- ...............
Pounds per I 8 EEEfcEEEEEEEEEEEEEE^EEEEEEEEEEEEE*? =>•-«"- ....... - .......
H.P. at Switchboard
FIG. 20.—Turbine economy curve.
stages for heating and process supplies. The arrangement is analogous to the drawing off of steam from the receiver of a compound engine (page 19).
STEAM PLANT AUXILIARIES
Pumps.—Boiler-feed pumps are of the plunger (direct-steam or power-driven) or rotary (centrifugal) type: the latter being driven by a steam turbine or electric motor. Steam-driven pumps are used when there is need of their exhaust for feed-water heating. Centrifugal pumps are generally more compact, and easier to maintain than plunger pumps.
Size.—For plunger pumps, single-acting, if dw = diameter of water plunger, inches, n = number of water cylinders, S = plunger speed, feet per minute, the discharge in cubic feet per minute is Snd^ -r- 366, less the leakage and slip. Power-driven pumps are usually single-acting; steam-driven usually double-acting. For double-acting pumps, double the value above. Steam-driven pumps are usually described by giving (1) diameter of steam piston, (2) diameter of water plunger, (3) stroke: thus, 6 by 4 by 6. The steam piston should be somewhat larger in diameter than the water piston so that the pump may function even when worn. Piston speeds are practically never over 100 ft. per minute: half this is a proper allowance. The outside packed-plunger type is more easily kept in good shape, and the pot-valve pump is best where gritty water is used. For hot water, pumps should be brass-fitted.
Centrifugal Pumps.—These contain spirally-bladed impellers which by